CL/Vulkan: Add fillWithPattern interface In CL, the buffer can be requested to filled with a pattern. Adding a pattern fill helper routine that fills up the buffer from CPU side. Bug: angleproject:42267074 Change-Id: I144e9b7c6f4d1263f21cabc2491c46e8951e604f Signed-off-by: Gowtham Tammana <g.tammana@samsung.com> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5916157 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>